In the Fourth Generation (4G) communication system, the next generation communication system, an active research has been conducted to provide users with services of various Qualities of Service (QoSs) that have data rates of about 100 Mbps. In particular, an active research has been conducted in the current 4G communication system to support high speed services that provide mobility and QoS for a Broadband Wireless Access (BWA) communication system such as a wireless Local Area Network (LAN) system and a wireless Metropolitan Area Network (MAN) system. The typical 4G communication systems are the Institute of Electrical and Electronics Engineers (IEEE) 802.16d communication system and the IEEE 802.16e communication system.
The IEEE 802.16d communication system and IEEE 802.16e communication system use an Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiple Access (OFDM/OFDMA) scheme in the physical layer. The IEEE 802.16d communication system is a system that only considers a current fixed state of a Subscriber Station (SS) (i.e., a state that does not consider the mobility of the SS) and a single cell structure. Unlike this, the IEEE 802.16e communication system is a system that considers the mobility of an SS in the IEEE 802.16d communication system. An SS that has mobility can be referred to as a Mobile Station (MS).
FIG. 1 illustrates a schematic structure of a conventional IEEE 802.16e communication system.
Referring to FIG. 1, the IEEE 802.16e communication system has a multi-cell structure, namely a cell 100 and a cell 150. The IEEE 802.16e communication system includes a BS 110 that takes charge of the cell 100, a BS 140 that takes charge of the cell 150, and a plurality of MSs 111, 113, 130, 151, and 153. Signaling between the BSs 110 and 140 and the MSs 111, 113, 130, 151, and 153 are performed using the OFDM/OFDMA scheme. Among the MSs 111, 113, 130, 151, and 153, the MS 130 is positioned in a boundary area between the cells 100 and 150, i.e., in a handover area. Accordingly, if the MS 130 moves further into the cell 150 in the midst of transmitting/receiving a signal with the BS 110, a serving BS of the MS 130 changes from the BS 110 to the BS 140.
The conventional IEEE 802.16e communication system carries out signaling transmission/reception through a direct link between a fixed BS and an MS as illustrated in FIG. 1 and, thus, can easily build a wireless communication link of high reliability between the BS and the MS. However, because the BS is fixed in position, the IEEE 802.16e communication system has low flexibility in constructing a wireless network and, thus, has difficulty providing an efficient communication service in a wireless environment that experiences great changes in traffic distribution or required calls.
To overcome these disadvantages, a multi-hop relay type data forwarding scheme can be applied to a general cellular wireless communication system such as the IEEE 802.16e communication system, using fixed Relay Stations (RSs), mobile RSs, or general MSs. A multi-hop relay wireless communication system can quickly cope with a change of the communication environment and reconstruct a network, and can more efficiently manage the entire wireless network. For example, the multi-hop relay wireless communication system can extend a cell service area and enhance a system capacity. That is, when the channel between a BS and an MS is in poor condition, the multi-hop relay wireless communication system can install an RS between the BS and the MS and build a multi-hop relay path through the RS, thereby providing the MS with a wireless channel that has an excellent channel state. Also, by using a multi-hop relay scheme in a cell boundary area that has a poor channel state from the BS, the multi-hop relay wireless communication system can provide a higher-speed data channel, and can extend a cell service area.
An intra-BS handover process of an MS in the multi-hop relay wireless communication system is described below. First, the MS communicates through a serving node and acquires information on a neighbor RS or a neighbor BS through a neighbor advertisement message that is periodically received from the serving node. Here, the serving node of the MS can be either an RS or a BS that controls the MS. For example, the RS is described below. Even when the serving node of the MS is an RS, the MS is controlled by a serving BS of the RS. After that, the MS performs a signal level measurement operation for the serving node and the neighbor RS or the neighbor BS that can be a target node, and transmits the signal level measurement result to the serving node. Then, the serving node of the MS transmits the signal level measurement result to the BS that controls the MS. The BS then determines whether there is a need for the MS to handover to the target node on the basis of the signal level measurement result of the MS.
If a need exists for the MS to handover to the target node, the BS sends a handover command message to the MS, via the serving node of the MS, to handover to the target node. At this time, the MS generates a key to use in the target node from identifier (ID) information of the target node that is included in the handover command message, includes the generated key within a ranging request message to communicate with the target node, and sends the ranging request message including the generated key to the target node. The target node then forwards the ranging request message to the BS. The BS transmits ID information of the MS and the ID information of the target node to a gateway. Here, the gateway is defined as an entity that includes a function for managing information on the key to be used by the MS in the target node. The gateway generates and stores a key to be used by the MS in the target node using the ID information of the target node, and transmits the key to the BS. After that, in response to the ranging request message of the MS, the BS generates a ranging response message that includes a Connection ID (CID) to be used by the MS and the key to be used by the MS in the target node, and sends the ranging response message to the MS via the target node. The MS can then perform communication through the target node using the CID and the key.
In each handover, the MS performs a process of updating control information to use during communication. Here, the control information of the MS includes a station ID, service flow and connection setting information of the MS, information on a key to be used by the MS in a target node, and so forth. As above, even when an MS performs a handover within the same BS, the MS updates control information to use during communication, and performs communication in a target node using the updated control information. However, when an MS performs a handover within the same BS, if the MS can continue to communicate using control information that had previously been used in a serving node, even in a target node without updating the control information, the MS can be provided with a seamless service without having to perform an unnecessary procedure between the gateway and the BS.
Accordingly, there is a need for performing an intra-BS handover by an MS that can distinguish an RS and a BS and continues to use control information, which had previously been used by the MS in a communication with a serving node, during communication with a target node within the same BS in a multi-hop relay broadband wireless communication system.